I am on my second listening of the discs in chronological order (sans The Garden of Arcane Delights EP, which is on backorder).

I noticed a big difference in SQ beginning with Aion, as compared with the first four. Is it me, my system, bad pressings, or are the first four not on a par with the rest?
No, it's not you or your equipment. The first DCD disc sonics are a murky mess. The EP gets better, but still is subpar. From there it get better and things settle into a high level at Aion.
Thanks for the info.

Just listened to Within the Realm of a Dying Sun. The SQ clearly is not as good as Aion and later.

However, this is one of the most astounding albums I have ever had the pleasure of experiencing.
Totally agree with the Photon!
enjoy your new cds!